nuclear fuels and materials - 151-2017-00l filenuclear fuels and materials - 151-2017-00l ⌸lecture...

WIR SCHAFFEN WISSEN – HEUTE FÜR MORGEN

Nuclear Fuels and Materials - 151-2017-00L

Manuel A. Pouchon :: Head of LNM :: Paul Scherrer Institut

Master of Nuclear Engineering ‐ Spring Semester 2016

Lecture 6: Lifetime Assessment, Repetition, …

Nuclear Fuels and Materials - 151-2017-00L ⌸ Lecture 6 - Page 2/73

• Lifetime assessment Bathtub curve Typical damage & loads Load approach, Van Mises stress, Notch ASME codes, design stresses/loads, design curves Risk, damage development NDE (None Destructive Examination)

• Repetition Phase diagrams Material properties, testing, improvement, damage Cladding

TOC


Requirement Tools

Well established, sound design Design codes

Establishment of long-term materials properties

Improve existing data base and understanding of related damage

Collecting experience from plants Provide methods and schedules for non destructive evaluation and condition based monitoring

Monitoring plant life Life management concept

Operating plant beyond design life Life extension concepts

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Safe and reliable operation of power plants


Exposure Micro-scale Macro-scale

Temperature Phase reactions, segregations Hardening, embrittlement, swelling

Irradiation Displacement damage, phase reactions, segregation, helium damage

Hardening, embrittlement, swelling

Environment Surface layer, local attack (pitting), grain boundary attack, formation of local stress raisers

Reduction of carrying cross section, sub-critical crack growth, unexpected premature failure

Impact and static load Dislocation movement, diffusion controlled dislocation and grain boundary processes

Plastic deformation, creep deformation, buckling, plastic collapse, sub-critical crack growth, premature (catastrophic) failure

Cyclic load Dislocation movement, local micro-crack formation, intrusions/extrusions

Cyclic softening, ratcheting, sub-critical crack growth, premature failure

Combined exposures: creep-fatigue, irradiation creep, corrosion fatigue, stress corrosion cracking

(Synergistic) damage accumulation (Synergistic) damage accumulation, unexpected damage, premature failure

Typical damage in nuclear plants


The internal pressure creates primary (or membrane) stresses in the wall. For an SFR membrane stresses are significantly lower but thermal induced secondary stresses become important.

W. Hoffelner, Materials for Nuclear Plants, p. 411, ISBN: 978-1-4471-2914-1 / http://www.n.t.u-tokyo.ac.jp/kasahara/homepage/Technolog

Loads occurring in a pressure vessel compared with loads occurring in an almost non-pressurized vessel.

Typical loads


The concept of a „local approach“. Mainly uniaxial laboratory data are applied to components using appropriate equivalent stresses or strains.

W. Hoffelner, Materials for Nuclear Plants, p. 412, ISBN: 978-1-4471-2914-1

Local approach


http://en.wikipedia.org/wiki/Von_Mises_yield_criterion

Equivalent stresses

van Mises stress criterion12

Tresca stress criterion

is “equivalent” for the material


The Neuber hyperbola for determination of stress–strain in a notch root

W. Hoffelner, Materials for Nuclear Plants, p. 416, ISBN: 978-1-4471-2914-1 / Neuber H (2001) Kerbspannungslehre, 4th edn. Springer, Be

Stresses in notches


• Section I Power Boilers• Section II Materials• Section III Rules for Construction of Nuclear

Power Plant Components• Section IV Heating Boilers• Section V Nondestructive Examination• Section VI Rules for the Care and Operation of

Heating Boilers• Section VII Guidelines for the Care of Power

Boilers• Section VIII Pressure Vessels• Section IX Welding and Brazing Qualifications• Section X Fiber-Reinforced Plastic Pressure

Vessels• Section XI Inservice Inspection of Nuclear Power

Plant Components• Section XII Rules for Construction and Continued

Service of Transport Tanks• Code Cases Rules for specific requirements or use

of materials not part of the current code version

American Society of Mechanical Engineers (ASME)

ASME-code


Low temperature (Section III Div. 1) High temperature (Section III Div. 5)

• Failure by plastic instability or necking• General structural collapse under a

single application of limit load• Time-independent buckling• Incremental collapse or ratcheting

under cyclic loading• Fatigue under cyclic loading• Fast fracture

• Creep rupture under sustained primary loading

• Excessive creep deformation under stained primary loading

• Cyclic creep ratcheting due to steady primary and cyclic secondary loading

• Creep fatigue due to cyclic primary, secondary, and peak stresses

• Creep crack growth and non-ductile fracture

• Creep buckling

Design cases


Primary stress (P) :The basic characteristic of a primary stress is that it is not self-limiting, cannot berelieved by localized plastic deformation, and if not limited, can lead toexcessive plastic deformation of the structure. Primary stress is an algebraic sumof general or local primary membrane stress (primary membrane stress, Pm, or localprimary membrane stress, PL ) and primary bending stress (Pb ) which is a bendingstress that is induced directly by the pressure load acting upon a specific geometryand is not induced by discontinuity conditions. The primary stresses are generallybased on linear elastic theory.

Secondary stress (Q):The basic characteristic of a secondary stress is that it is self-limiting, because itcan be relieved by small-localized plastic deformation that cannot cause largedistortion of the structure. Failure from one application of a secondary stress is notexpected. Not all deformation-controlled stress can be categorized as secondarystress. The code requires all deformation-controlled stress with high elastic follow-upto be treated as primary stress.

Peak stress (F):The basic characteristic of a peak stress is that it does not cause any noticeabledistortion. The peak stress is objectionable only as a possible source of a fatiguecrack or a brittle failure.

Different design stresses


Design Loadings:The specified design parameters for the Design Loadings category equal or exceed those of the most severe combination of coincident pressure, temperature, and applied loads specified under events that cause Service Level A loadings described next.

Service Level A Loadings (Normal operation):These are loadings arising from system startup, operation in the design power range, hot standby, and system shutdown. Does not include service loadings covered by Levels B, C, and D or Test Loading.

Service Level B Loadings (upset conditions): These are deviations from Service Level A loadings that are anticipated to occur at moderate frequency. The events that cause Service Level B loadings include transients which result from any single operator error or control malfunction, transients caused by a fault in a system component requiring ist isolation from the system, and transients due to loss of load or power. These events include any abnormal incidents not resulting in a forced outage.

Service Level C Loadings (emergency conditions): These are deviations from Service Level A loadings that have a low probability of occurrence and would require shutdown for correction of the loadings or repair of damage in the system. The total number of postulated occurrences for such events may not exceed 25. 10

Service Level D Loadings (faulted conditions):These are the combinations of loadings associated with extremely low probability, namely, postulated events whose consequences are such that the integrity and operability of the nuclear energy system may be impaired to the extent that only consideration of public health and safety are involved.

Test Loadings :These are pressure loadings that occur during hydrostatic tests, pneumatic tests, and leak tests. Other types of tests are classified as Service Level A or B loading. If any elevated temperature tests are specified as Test Loadings for a component, then these loadings shall be considered as part of Service Level B loadings.

Different loads


Temperature dependence of allowable stresses as given in the ASME-code. The maximum allowable stress is the lower envelope of the curves (TS…tensile stress at temperature,YS…yield stress at temperature, creep…appropriate creep stress)


Typical design curve


Section IID Table 1A,1B SI Metric Units Term

0Specifications (Enter size range here)(Enter size range here)(Enter size range here) 1Type/Grade 2Min TS in B6 (MPa) 415 Metric is 585 If CU spec the soft conversion will appear in B6 3Min YS in B7 (MPa) 205 Metric is 415 If CU spec the soft conversion will appear in B7 4

5Ratio/Stress=A+B(T-T0)+C(T-T0)^2+D(T-T0)^3+E(T-T0) 4̂+F(T-T0)^5 TermA B C D E F T0 (C) 0

Yield Ratio 1 -1.95797E-03 1.32927E-06 1.27212E-08 -2.53972E-11 7.37502E-15 21 1Tensile Ratio 1 1.43636E-03 -3.37503E-05 1.74414E-07 -3.60593E-10 2.58562E-13 21 2Enter .67AvCrpRpt " 3Enter .8MinCrpRpt " 4Enter 1%Crp10^5 " 5

Temperature deg C 21 40 65 100 125 150 175 200 225

Min YS Ratio, Ry 1.000 1.000 0.917 0.859 0.822 0.790 0.763 0.740 0.723MinYS, SyRy (Y-1) ($B$7)*(C$21) 205 205 188.1 176.1 168.5 162.0 156.4 151.8 148.1Min TS Ratio, Rt 1.000 1.000 1.011 0.976 0.941 0.907 0.877 0.853 0.836Min TS, StRt ($B$6)*(C$23) 415.0 415.0 419.7 404.9 390.7 376.6 364.1 354.1 347.01.1*Min TS., 1.1StRt (U) 1.1*(C24) 415.0 415.0 415.0 415.0 415.0 414.2 400.5 389.6 381.6Av Rupt in 10 ̂hrsMin Rupt in 10 5̂ hrs

0.9 SyRy 0.9*(C22) 184.5 184.5 169.3 158.5 151.7 145.8 140.7 136.6 133.32/3 SyRy (2/3)*(C22) 136.7 136.7 125.4 117.4 112.4 108.0 104.3 101.2 98.7St/3.5 ($B$6)/3.5 167.4 167.4 118.6 118.6 118.6 118.6 118.6 118.6 118.61.1StRt/3.5 1.1*(C24)/3.5 130.4 184.2 131.9 127.2 122.8 118.4 114.4 111.3 109.02/3 Sy (2/3)*($B$7) 136.7 136.7 136.7 136.7 136.7 136.7 136.7 136.7 136.70.67Av Creep Rupt0.8Min Rupt1% Creep in 10^5Hrs"F" factor

Allowable Stress - Hi MIN(C$29,C$31 130 137 119 119 119 118 114 111 109Allowable Stress - Lo MIN(C$30,C$3 130 137 119 117 112 108 104 101 99

Allowable Stress * 0.85 - H=0.85*C39 111 116 101 101 101 101 97 95 93Allowable Stress * 0.85 - L=0.85*C40 111 116 101 100 96 92 89 86 84

Example for ASME data sheet


Example for materials data scatter and evaluation curves. Solid line ASME Y-1 Tables for this type of material, dashed line EURONORM for this type of material, dotted line calculated average.

W. Hoffelner, Materials for Nuclear Plants, p. 429, ISBN: 978-1-4471-2914-1 NIMS metallic materials (2011) Low alloy steels 1 Cr 0.5 Mo http://metallicmaterials.nims.go.jp/metal/view/resultMetalList.html?id=48205401_sc0.

Design curves




TOC



Typical risk diagram with classes of probability of failure and of consequences. Isorisk lines connect areas with comparable riks

Risk considerations


W. Hoffelner, Materials for Nuclear Plants, p. 410, ISBN: 978-1-4471-2914-1 /

Bakirov M (2010) Impact of operational loads and creep, fatigue corrosion interactions on nuclear power plant systems, structures and components (SSC). In: Tipping PG (ed) Understanding and mitigating ageing in nuclear power plants. Woodhead, pp 146–188

Schematic of damage development in nuclear plants; ISI means in service inspection

Structural Integrity of Primary Boundary Components

Damage often accumulates at local stress raisers. Also flaws and imperfectionsalready existing in the material or weldments can act as crack starters. Once these cracks reach a critical size catastrophic failure can occur. The lower line refers to the real crack length and how it develops with time. The upper line refers to the critical crack length at which the component fails. The critical crack length is not a constant because effects like thermal embrittlement or thermal ageing can reduce the fracture toughness and therefore also reduce the critical crack length. NDE important

Development of Damage


Wüstenberg H, Erhard A, Boehm R (2011) Limiting factors for crack detection by ultrasonic investigation. BAM, Berlin, Germany http://www.ndt.net/article/0198/wues_lim/wues_lim.htm.


As NDE deals mainly with cracks it is strongly linked with fracture mechanics as shown above. A general scheme for the definition of recording thresholds and acceptability levels for an NDT method is shown.

Connection between NDE-analyses and fracture mechanics


• Ultrasonic (UT)• Eddy current (ET)• Magnetic particle (MT)• Liquid penetrant (PT)• Radiography (RT)• Visual (VT)

• OthersLeak testing (LT)Surface replicationAcoustic emission (AE) Probability of detection (POD) curve

(solid line) with lower 95 % confidence band (dashed line)

Wüstenberg H, Erhard A, Boehm R (2011) Limiting factors for crack detection by ultrasonic investigation. BAM, Berlin, Germany http://www.ndt.net/article/0198/wues_lim/ wues_lim.htm.


Good introduction: http://www.ndt- ed.org/ AboutNDT/aboutndt.htm

Non-destructive testing methods


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Ultrasonic testing: In ultrasonic testing, high-frequency sound waves are transmitted into a material to detect imperfections or to locate changes in material properties. The most commonly used ultrasonic testing technique is pulse echo, whereby sound is introduced into a test object and reflections (echoes) from internal imperfections or the part's geometrical surfaces are returned to a receiver.

Eddy current testing:

NDE testing methods


plate

crack

0 2 4 6 8 10

initial

pulse

crack

echo

back surface

echo

Oscilloscope, or flaw detector screen

High frequency sound waves are introduced into a material and they are reflected back from surfaces or flaws.

Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen showing the depth of features that reflect sound.

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Ultrasonic testing


Conductivematerial

CoilCoil's magnetic field

Eddy currents

Eddy current's magnetic field

Eddy Current Testing I


Magnetic Field

From Test Coil

Magnetic Field From

Eddy Currents

Eddy Currents

Crack

Cracks cause a disruption in the circular flow patterns of the eddy currents and weaken their strength. This change in strength at the crack location can be detected.

Change in impedanceScreen of multi-frequency instrument during inspection.

Eddy Current Testing II


Top view of developed film

X-ray film

The part is placed between the radiation source and a piece of film. The part will stop some of the radiation. Thicker and more dense area will stop more of the radiation.

= more exposure

= less exposure

The film darkness (density) will vary with the amount of radiation reaching the film through the test object.

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Radiography


The part is magnetized. Finely milled iron particles coated with a dye pigment are then applied to the specimen. These particles are attracted to magnetic flux leakage fields and will cluster to form an indication directly over the discontinuity. This indication can be visually detected under proper lighting conditions.

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Magnetic Particle Inspection


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• A liquid with high surface wetting characteristics is applied to the surface of the part and allowed time to seep into surface breaking defects.

• The excess liquid is removed from the surface of the part.

• A developer (powder) is applied to pull the trapped penetrant out the defect and spread it on the surface where it can be seen.

• Visual inspection is the final step in the process. The penetrant used is often loaded with a fluorescent dye and the inspection is done under UV light to increase test sensitivity.

Liquid Penetrant Inspection


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Most basic and common inspection method.

Tools include fiberscopes, borescopes, magnifying glasses and mirrors.

Portable video inspection unit with zoom allows inspection of large tanks and vessels, railroad tank cars, sewer lines

Robotic crawlers permit observation in hazardous or tight areas, such as air ducts, reactors, pipelines.

Visual Inspection




TOC


• Phase Diagrams

• Iron-carbon alloy phases

Repetition


Iron Carbon Phase Diagram


Time-Temperature-Transformation

TTT diagram for carbon steels


The structure of pure iron. Has a body-centred cubic (BCC) crystal structure. It is soft and ductile and imparts these properties to the steel. Very little carbon (less than 0.01% carbon will dissolve in ferrite at room temperature). Often known as iron.

A photomicrograph of 0.1% carbon steel (mild steel). The light areas are ferrite.

Ferrite


High temperature structure of pure iron:This is the structure of iron at high temperatures (over 912 °C). Has a face-centre cubic (FCC) crystal structure. This material is important in that it is the structure from which other structures are formed when the material cools from elevated temperatures. Often known as iron. Not present at room temperatures.

Austenite


A compound of iron and carbon, iron carbide (Fe3C).

It is hard and brittle and its presence in steels causes an increase in hardness and a reduction in ductility and toughness.

Cementite


A laminated structure formed of alternate layers of ferrite and cementite.

It combines the hardness and strength of cementite with the ductility of ferrite and is the key to the wide range of the properties of steels. The laminar structure also acts as a barrier to crack movement as in composites. This gives it toughness.

Two-dimensional view of pearlite, consisting of alternating layers of

cementite and ferrite.

Pearlite


©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

The evolution of the microstructure of hypoeutectoid and hypereutectoid steels during cooling. In relationship to the Fe-Fe3C phase diagram.

Fe-C diagram: Hypo- & Hpyer-Eutectoid


Bainitic steel


A very hard needle-like structure of iron and carbon.Only formed by very rapid cooling from the austenitic structure (i.e. above upper critical temperature). Needs to be modified by tempering before acceptable properties reached.

The needle-like structure of martensite, the white areas are retained austenite.

Body Centered Tetragonal Unit Cell

Martensite – What is it, how does it form


When martensite is tempered, it partially decomposes into ferrite andcementite. Tempered martensite is not as hard as just-quenched martensite,but it is much tougher. Note also that it is much finer-grained than just-quenched martensite.

Tempered Matertensite


Material properties

& testing

& damage

Repetition


http://www.msm.cam.ac.uk/doitpoms/

Critical resolved shear stress (Schmids Law)


Upper and lower yield stressContinous yielding

Typical Stress-Strain Curves


Low temperature

lattice resistance

discrete obstacles resistance

High temperature

Power-law creep involving cell-formation by climb

Power-law breakdown: glide contributes increasingly

Dynamic recrystallization replaces deformed by undeformed material

Diffusional flow by diffusional transport through and round the grains

Overview: Plastic Deformation


See also : Impact testing

http://www.twi.co.uk/technical-knowledge/job-knowledge/job-knowledge-71-mechanical-testing-notched-bar-or-impact-testing/

Impact Testing


Fracture Toughness: a quantitative impact measure


S-N curve (Wohler S-N diagram):nominal stress amplitude S versus cycles to failure N

http://www.fea-optimization.com/ETBX/stresslife_help.html

Material (Curve ) A:endurance limit which represents a stress level below which the material does not fail and can be cycled infinitely. e.g. Steel & Ti

Material (Curve ) B:do not exhibit well-defined endurance limits. These materials instead display a continuously decreasing S-N response. Fatigue strength Sffor a given number of cycles must be specified.e.g. non-ferrous metals and alloys (Al, Cu, Mg, ..)

http://www.energy.kth.se/compedu/webcompedu/WebHelp/S5_Aeroelasticity/B1_Introduction_to_Aeroelasticity/C7_Introduction_to_High_Cycle_Fatigue/ID122_files/S-N_diagram.htm

Fatigue curves


Mechanism At Room Temperature At high Temperature

Grain hardening Fully operative Diffusion processes and grain boundary sliding become important, large grains show better properties

Dislocation hardening operative Annealing of dislocationSolid solution strengthening

operative operative

Particle strengthening Orowan bowing or cutting Mainly climbingOrder effects Moderate influence Dislocation movement

through ordered lattice difficult due to diffusion effects

Strengthening of metallic materials


http://hss.energy.gov/nuclearsafety/techstds/docs/handbook/h1019v1.pd

Neutron Spectra of Thermal and Fast Reactors


Comparison of MD simulations of displacement cascades in Fe for different PKA energies

http://dx.doi.org/10.1063/1.1880013

Cascade dependency on energy


Which damage in which temperature region


Wiedersich H (1986) In: Physics of radiation effects in crystals Elsevier 237

Dth: Thermal diffusion

Drad: radiationinduceddiffusion

Dm: ion mixing

• At high temperatures thermal diffusion is predominant.

• Radiation induced diffusion depends on the density of sinks. Sinks reduce the amount of excess pointdefects which decreases the respective diffusion coefficient as shown here with „no sinks“, p=10-4 and p=10-3.

• Ion mixing which happens at low temperatures independent of the temperature will not further bediscussed here.

Temperature & radiation induced diffuison


http://dx.doi.org/10.1016/0022-3115(84)90626-3

General form of swelling versus dose with the various stages involved.

Void Swelling


Thermal creep testing


• High temperature progressive deformation of a material at constant stress is called creep.• High temperature is a relative term that is dependent on the materials being evaluated.• A typical creep curve is shown below:

In a creep test a constant load is applied to a tensile specimen maintained at a constant temperature. Strain is then measured over a period of time. The slope of the curve, identified in the figure, is the strain rate of the test during stage II or the creep rate of the material. Primary creep, Stage I, is a period of decreasing creep rate. Primary creep is a period of primarily transient creep. During this period deformation takes place and the resistance to creep increases until stage II.Secondary creep, Stage II, is a period of roughly constant creep rate. Stage II is referred to as steady state creep.Tertiary creep, Stage III, occurs when there is a reduction in cross sectional area due to necking or effective reduction in area due to internal void formation.

Creep – Creep Stages

http://www.materialsengineer.com/CA-Creep-Stress-Rupture.htm


Creep Stages


kT

QneB

Irradiation creep

Biased flow of point defects (interstitials and vacancies) to sinks

Thermal Creep

Dislocation slip and climb

Diffusion flow

Grain boundary sliding

strongly temperature‐dependence

power law stress‐dependence

n=1 or 2 ?

m 1 or 1/2 ?

Principle of Creep

mnKB

SDBB 0

K: dpa / rate

Thermal Creep – Irradiation Creep


Norton‘s Creep Lawσ = A. ε̇n . exp (U/kT)

Monkman Grant Rulet F . ε̇ = Const

ε̇…. secondary creep ratet F … time to fracture

Important creep laws


Types of Corrosion


Different types of oxide layers. Dense, protective layer at the left side and a porous layer at the right side. The porous layer can easily spall off and it also allows penetration of corrosive speciei.

https://192.107.58.30/D19/Heikinheimo.pdf

Development of Surface Layers


Main mechanisms of irradiation assisted stress corrosion cracking

http://dx.doi.org/10.1016/S0022-3115(99)00075-6

Mechanisms of IASCC (Irradiation Assisted Stress Corrosion Cracking)


• Cladding

Repetition


PelletFuel

CladdingFuel tube

Fuel rod Assembly

Introduction – From the pellet to the assembly


Hexagonal structure• Less gliding planes than cubic lattice• Distinct formation of

twin boundaries Complex behavior under

plastic deformation Strong anisotropy Strong formation of structure

Thermo-mechanical fabrication process is essential for the evolution the microstructure, the mechanical properties and the corrosion resistance

Hexagonal lattice..ABABCBCBCBCBABA..(= Stacking fault)

= Twin

Zirconium – Mechanical Properties


The extruded tube is then cold pilgered

K. Baur, 2002

Zirconium/Cladding – Fabrication XIV


Radial orientation of c-axis due to high reduction in diameter (beneficial for later hydride precipitation):

K. Baur, 2002

Zircaloy Cladding – Texture I


Radial orientation of c-axis due to high reduction in diameter (beneficial for later hydride precipitation):

K. Baur, 2002

Zircaloy Cladding – Texture II


wt% Zr Sn Fe Cr Ni Nb O

Zircaloy-2 Bal. 1.2-1.7 0.07-0.2 0.05-0.15 0.03-0.08 - 0.1-0.14

Zircaloy-4 Bal. 1.2-1.7 0.18-0.24 0.07-0.13 0.007 max - 0.1-0.14

ZIRLO Bal. 1.0 0.1 - - 1 ca 0.1

M5 Bal. - 0.015-0.006 - - 0.8-1.2 0.09-0.12

Zr-2.5Nb Bal. 0.05 max 0.15 max 0.02 max 0.007 max 2.4-2.8 0.09-0.13

Zircaloy – Some Alloys


Before

IrradiationAfterIrradiation

• Pellet swelling• Pellet bambooing• Pellet cracking• PCMI• Iodine release

B.R.T. Frost (Ed), 1994, Nuclear Materials, Vol. 10B, Materials Science and Technology, VCH, p.43

PCMI IV – Pellet cracking during irradiation


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PCI II: Stress concentration at cracks


• Debris fretting is the most common failure cause for leakers

• Debris are caught in the spacer

Westinghouse Atom

Debris fretting


Distribution due to texture

Hydrides: “Normal” hydride distribution


Irradiation damage: Growth

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